Since the first test-tube baby was born in 1979, various methods for assisted reproduction technology (ART) have been developed and applied to the treatment of sterile patients. Examples of ART are in vitro fertilization-embryo transfer (IVF-ET), intracytoplasmic sperm injection (ICSI), testicular sperm extraction (TESE), round spermatid injection (ROSI) and-embryo freezing. While ART is an important and general method for the treatment of sterile patients, there remain problems to be overcome, such as high costs, complicated procedure and low chance of success.
The use of ART is on the increase. The rate of pregnancy in IVF has increased but is not up to the expectation. The actual take home baby rate is 15-30%. According to the U.S. statistics, the pregnancy rate and delivery rate per cycle by using IVF in 1996 was 23.8% and 19.3% respectively. In 1997 statistics, these rates increased to 29.3% and 24.0% each. However, there was no substantial difference between 1996 statistics and 1997 statistics.
The successful human pregnancy is dependent upon follicular development, number of oocytes retrieved, fertilization, embryo development and implantation, during an assisted reproductive technology (ART) cycle (Sakkas D, et al., 2001). Among them, blastocyst implantation into the human uterus is a complex process dependent on profound structural changes in the endometrium and the developing embryo. Tissue remodeling is requisite to uterine preparation, embryonic breaching of the epithelial basement membrane and subsequent penetration of the endometrial stroma.
It is thought that matrix metalloproteinases (MMPs) are essential for the breakdown of extracellular matrix (ECM) components during this process. MMPs are an important family of zinc-dependent enzymes with a broad range of substrate specificities capable of the breakdown of extracellular matrix (Hulboy et al., 1997). Many studies suggest that the MMPs play an important role in tissue remodeling and tissue repair under various physiological and pathological conditions such as morphogenesis, ovulation, angiogenesis, arthritis, wound healing and tumor invasion. (Behrendtsen et al., 1992: Cross et al., 1994; Lefebvre et al., 1995; Harvey et al., 1995; Leco et al., 1996; Alexander et al., 1996) However, little is known about the physiological regulation of MMPs and the mechanism whereby these proteases are activated in vivo.
Collagenolytic enzymes, particularly MMPs, are thought to play a vital role in ovulation in other species. Examples include the fibrillar collagenases such as MMP-1, which break down the fibrillar collagen forms that confer much of the structural integrity to the ovarian stroma. Expression of MMP-9, also known as 92 kDa type IV collagenase/gelatinase B, has also been detected in mouse and human pre-implantation embryos, EC cells, and blastocyst outgrowths by zymography, immunocytochemistry, and PCR. Culture of blastocyst outgrowths in the presence of fibroblast growth factor-4 increased secretion of MMP-9. MMP-9 has been shown to be developmentally regulated in mouse blastocysts and cytotrophoblast cells during embryo implantation. On the other hand, successful pregnancy is dependent upon invasion of trophoblast into the decidua at implantation, and subsequently the further invasion of extravillous trophoblast into the walls of the maternal spiral arterioles (Fisher et al., 1985; Librach et al., 1991; Cross et al., 1994). These events require the breakdown of extracellular matrix and cellular migration. In rat and human fetal membranes, the amount of MMP-9 is increased with labour (Bryant-Greenwood and Yamamoto, 1995; Draper et al., 1995; Lei et al., 1995).
Among MMPs, the MMP-9, degrades a variety of extracellular matrix components including many kinds of collagens (IV, V and XI), elastin, proteoglycan and gelatin (Hibbs et al., 1985: Murphy et al., 1991). Moreover, previous studies have demonstrated that the secretion of MMP-9 from human cervical fibroblasts (Sato, H. and Seiki, M., 1993), trophoblasts (Shimonovitz, S. et al., 1996) and endometrial stromal cells (Huang, H. A., et al., 1998) is stimulated by cytokines and hormones. MMP-9 has been suggested to intervene at different stages of the cyclical changes in female reproduction (Jeziorska, M., et al., 1996; Librach, C. L. et al. 1991; Vadillo-Ortega, F. et al., 1995), such as in the menstrual cycle, ovulation, implantation, parturition, and involution of the mammary glands after lactation. Ovulation is a process triggered by the preovulatory surge of LH from the pituitary gland, which results in the liberation of the mature ovum from the preovulatory ovarian follicle. Additionally, ovulation is probably a result of controlled enzymatic degradation and loss of collagen in the follicle wall (Espey, 1994; Luck and Zhao, 1995). Although this process requires extensive tissue remodeling, and MMP-9 is important for generating the proteolytic activity needed at the time of ovulation, little is known about the relationship between MMP-9 and follicular fluid of human. The presence of MMP-9 in follicular fluid, which have substrate specificities that include the basement membrane constituent collagen IV, indicates that they are likely to be required for tissue remodeling during follicle growth and development.